Field
This telecommunication device, software module, system or business method relates generally to the field of telecommunication.
Description of the Related Art
The current global telephone network, the PSTN (Public Switched Telephone Network), is built for voice communication of limited bandwidth (only 3.5 kHz). Broadband networks, e.g. the Internet, can also be used for real-time person-to-person communication, e.g. voice communication, often called VoIP (Voice over Internet Protocol). The Internet transports data between endpoints, regardless of the data content or the application and is therefore called a transport network.
Although such technology has the potential of multimedia communication beyond the Plain Old Telephony Service (POTS), e.g. video, presence and instant messaging, VoIP has been used by telecom operators to replace pieces of the PSTN, still only offering POTS. Many telecom operators have built their own VoIP network using softswitches and session border controllers (SBCs). These local VoIP networks primarily connect to each other for voice traffic, counting voice minutes for billing as part of an intermixed transport and business architecture, sometimes called Session Delivery Network (SDN).
IMS (Internet protocol Multimedia Subsystem) is one type of SDN. SDN and what is here described, applies to both fixed and wireless networks. Even Voice over LTE (Long-Term Evolution), (VoLTE), as defined for the telephony service over 4G (fourth generation) wireless networks, is an SDN.
SDN is based on specific services—mostly voice in form of plain telephony—being handled separately from other data that are transported by an overlay of various servers on top of general IP (Internet Protocol) networks. The SDN uses hardware and software, e.g. in form of softswitches and SBCs, while handling the signaling (the connection of parties) as well as when transporting the media (the packetized voice data).
The SDN transports a call through the overlay servers, instead of directly between the communicating parties, which a global transport IP network would be able to do without the overlay.
Furthermore, telephony type of services must be delivered into private IP networks, LANs (Local Area Networks) behind firewalls with their NATs (Network Address Translators). Firewalls generally block such communication, an issue that either has to be resolved by E-SBCs (Enterprise Session Border Controllers) at the edge of the private network or by some workaround method such as e.g. STUN (Session Traversal Utilities for NAT, RFC 5389), TURN (Traversal Using Relays around NAT, RFC 5766), ICE (Interactive Connectivity Establishment, RFC 5245) or far end NAT traversal. Far end NAT traversal use similar methods as the mentioned RFC recommendations, but initiated from the service side rather than the client side. RFCs (Request For Comments) are Internet standards defined by the IETF (Internet Engineering Task Force).
However, such workaround methods have drawbacks in generality and reliability and are generally based on keep-alive packets to keep paths open for incoming calls through the firewall, that reduce the battery stand-by time of mobile devices, since their sleep mode will not be utilized.
VPN (Virtual Private Networks) in form of private IP lines e.g. over MPLS (Multiprotocol Label Switching), or encrypted tunnels over public networks are sometimes used to resolve the NAT and firewall traversal issue more centrally in the network. In addition, VPN solutions are complex, costly and introduce problems and restrictions in themselves, by not utilizing the advantages provided by a global quality transport network. Furthermore, VPN solutions introduce security issues when the private LAN of the customer is moved into the service provider's space, often resulting in that customers want a firewall towards the VPN, again introducing the problems with real-time communication that the VPN solution was supposed to resolve.
The SDN, but not a global transport network like the Internet, may achieve the following functions: (i) allowing service providers to bill for their services, (ii) using a higher quality for real-time traffic than the best effort quality available over the Internet, (iii) only allowing subscribers to the joined group of service providers to participate in the communication, (iv) fulfilling lawful intercept requirements and (v) fulfilling emergency calling requirements.
In the SDN as well as the old PSTN, most of these functions are realized centrally inside the service provider's network.